Dynamic control by intertube coupling devices



April 23, 1935. J. H. HAMMOND, JR

DYNAMIC CONTROL BY INTERTUBE COUPLING DEVICES Filed Feb. 15, 1933 3Sheets-Sheet 1 April 23, 1935. J. H. HAMMOND, JR 1,993,520

DYNAMIC CONTROL BY IIITERTUBE COUPLING DEVICES Filed Feb. 15, 1955 3Sheets-Sheet 2 \J gnveniioi flame/1 1 5 yzw 47 4%. 2

April 23, 1935.

J. H. HAMMOND, JR

DYNAMIC CONTROL BY INTERTUBE COUPLING DEVICES Filed Feb. 15, 1933 3Sheets-Sheet 3 Patented Apr. 23, 1935 UNITED STATES PATENT OFFICEDYNAMIC CONTROL BY INTERTUBE COUPLING DEVICES Application February 15,1933, Serial No. 656,813

14 Claims.

The invention relates to amplifying systems used for reproducing musicor speech from sound records and more particularly to means forcontrolling the gain ratio of .such amplifying systems.

According to the invention, the gain ratio of a multi-stage vacuum tubeamplifier is controlled by varying the impedance of the coupling betweenstages. This does not change the operating points of the tubes. Thisimpedance may include another vacuum tube which will be called, forpurposes of description, a coupling tube. The impedance of this tube maybe controlled by the potential of its grid which, in turn, may becontrolled by the dynamics of the sound fed to the amplifier.

The control of the gain ratio may be such as to amplify the louder notesmore in proportion than the softer notes. This is often desirable inreproducing sound from a sound record or talking film where normally thecontrast between loud and soft notes is not sufiiciently emphasized forperfect reproduction. Or, the gain ratio control may be arranged to havejust the opposite effect, that is, to amplify the softer notes more inproportion than the louder notes. If desired, a reversing switch may beprovided so that the amplifier be changed from one type of operation tothe other immediately.

The invention also consists in certain new and original features ofconstruction and combination of parts hereinafter set forth and claimed.

Although the novel features which are believed to be characteristic ofthis invention will be particularly pointed out in the claims appendedhereto, the invention itself, as to its objects and advantages, and themanner in which it may be carried out, may be better understood byreferring to the following description taken in connection with theaccompanying drawings forming a part thereof, in which Fig. 1illustrates diagrammatically a circuit 7 according to the invention;

Figs. 2 to 4, inclusive, illustrate modified circuits having differenttypes of variable impedance intertube coupling devices; and

Fig. 5 illustrates diagrammatically the operation of the circuit shownin Fig. 1.

In the following description and in the claims, various details will beidentified by specific names for convenience, but they are intended tobe as generic in their application as the art will permit.

Like reference characters denote like parts in the several figures ofthe drawings.

In the drawings accompanying and forming part of this specification,certain specific disclosure of the invention is made for purposes ofexplanation, but it will be understood that'the details may be modifiedin various respects without departure from the broad aspect of theinvention.

Referring now to the drawings, and more particularly to Fig. l, thesystem as shown comprises the amplifier tubes 22, 24, 21 and push pullamplifier 44 of a multi-stage vacuum tube amplifier. Tube 25 constitutesthe coupling tube for varying the impedance of the coupling betweentubes 24 and 21.

Sound energy is supplied to the amplifier tube 22 from a sound recordwhich may be either on a moving film or on a rigid wax record.

In the drawings, light from a source [0 is focused by a lens H throughan aperture l2 in the aperture plate 3 upon the sound track of a. movingfilm M. The light which passes through the film I4 is focused by meansof a lens H4 upon a photoelectric cell l5 which changes the lightvariations into electrical variations. These variations pass throughtransformer I 6 to the double-pole double-throw I switch I I.

For receiving sound from a disk or other wax record (not shown) apick-up I8 is providedwhich is also connected to a double-poledoublethrow switch ll. By operating switch I! sound from either type ofrecord may be reproduced.

The switch I! is connected to a transformer 2| which is connected in theinput circuit of amplifier tube22. The output circuit of tube 22 isconnected to the input circuit of amplifier tube 24 through atransformer 23.

Connected to the output circuit of amplifier tube 24 is a choke coil 3|.In parallel therewith is the coupling tube 25. The choke coil 3| andcoupling tube 25 are connected to the input of the next amplifier tube2'! through a blocking condenser 26.

It will be noted that the plate circuit of coupling tube 25 and thechoke coil 3| are in parallel and that variations in the impedance ofthe plate circuit of coupling tube 25 will vary the gain ratio of theamplifier.

change of coupling impedance in the plate circuit of the tube 24.

For controlling the impedance of coupling tube 25 a control tube 28 isprovided whose input circuit is connected to the input circuit ofamplifier tube 24. The output of control tube 28 is fed throughtransformer 29 to a rectifier circuit, including rectifier 35. Connectedin circuit with the rectifier 35 through a 3-pole double throw reversingswitch 36 is a biasing resistance 31 across which is connected acondenser 38.

C batteries 4| and 42 are connected to the reversing switch 36 and tothe biasing resistance 31 so that the bias on the grid of the couplingtube 25 is determined by the battery bias, and the variable bias due torectified current through resistor 31. C battery 34 gives the properbias to the amplifier tube 21 through resistance 35. The A battery forsupplying cathode heating current to the several tubes is denoted by 32and the B battery for supplying plate current to the tubes 21, 24, 25and 28 is denoted by 33.

The output of the amplifier tube 21 is then fed through transformer 43to a push pull amplifier 44 which in turn feeds a loud speaker 46through a transformer 45. The stationary coil of the loud speaker isdenoted by 41 and is energized by a source of direct current, indicatedby 48.

In the operation of the circuit shown in Fig. 1, the switch I1 is throwneither up or down, according to whether it is desired to receive aselection from the moving film I4 or the pick-up I8. In either case thesound energy is amplified by the tube 22 and then impressed upon thenext stage 24. The energy is further amplified by tube 24 and isimpressed by means of the coupling devices 3| and 25 upon the next stage21 where the energy is further amplified and fed to the push pullamplifier 44 which in turn feeds the loud speaker 46 in a manner whichwill be apparent to those skilled in the art.

The gain ratio of the multi-stage amplifier is controlled by varying theimpedance of coupling.

tube 25. This is done by the energy which is amplified by the controltube 28 and which is rectified by the rectifier 35 and which passesthrough the biasing resistance 31 in a'direction depending upon theposition of switch 36.

When the switch 36 is in its upper position the multi-stage amplifieracts as a volume expander. In other words, it so affects the dynamics ofthe sound impressed upon the amplifier that it amplifies the loud notesmore in proportion than the soft tones.- When the switch 36 is in itslower position the multi-stage amplifier operates as a volume compressorand amplifies the loud notes less in proportion than the soft notes.

When the switch 36 is in the upper position the current from therectifier passes through the biasing resistance in the direction of theupper arrow 5|. The C battery 4| is in series with the resistance 31 andassists the latter in impressing a negative bias upon the grid ofcoupling tube 25. The louder the sound the more current will flowthrough the biasing resistance 31 and the greater will become thenegative bias on the coupling tube. This raises the impedance of thecoupling tube 25 which increases the voltage impressed upon the nextstage tube 21, which increases the amplification of the louder notesmore than the soft notes.

When the switch 36 is thrown to its lower position the current throughthe biasing resistance 21 flows in the direction of the lower arrow 52and both C batteries 4| and 42 are connected so as to oppose theresistance drop in resistance 31. Together, batteries 4| and 42 andresistance 31 control the bias upon the grid of the coupling tube 25.

In this case, the louder the sound, the greater will be the flow ofcurrent through the resistance 31. This will result in a decrease in thebias on the grid of coupling tube 25. This decreases the impedance ofcoupling tube 25 which increases the flow of plate current there throughand decreases the potential impressed upon the next amplifier stage tube21, resulting in a decrease in amplification with an increase in soundenergy, and vice versa.

Fig. 5 illustrates diagrammatically the operation of the circuit shownin Fig. 1. In this figure the impressed signal is represented by thealternating current source I23 and the internal impedance of theelectron discharge device 24 is represented by the resistance I24. Thechoke coil 3| is represented by the variable inductance I3I and theelectron discharge device 25 by the variable resistance I25.

The system shown in Fig. 1, the operation of which is diagrammaticallyshown in Fig. 5. varies from other similar systems in that the impedanceof the device 24, as represented by the resistance I24, remainssubstantially constant and the entire control is exercised by varyingthe coupling devices, represented by the variable inductance I3I and thevariable resistance I25, between the stage 24 and the subsequent stage21.

If desired, the choke coil 3| may be replaced by a non-inductiveresistance, making the circuit resistance-coupled instead ofinductance-coupled.

The operation of this modified form will be obvious from the descriptionabove.

Referring to Fig. 2, it will be seen that in place of an inductancecoupling between amplifier tubes 24 and 21 a transformer 6| is provided.The coupling tube 25 is connected across the primary of the transformer6| and operates to control the potential across the next stage tube 21in a .manner similar to that described above.

Referring now to Fig. 3, the amplifier tubes 24 .and 21 are transformercoupled and a variable voltage transfer from secondary winding of transiformer 6| to the grid of the tube'21.

Referring now to Fig. 4, amplifier tubes 24 and 21 are shown as coupledtogether by an inductance 66.. The iron core of this inductance is alsowound with a winding 68 which receives rectified current from therectifier 35, this current flowing in a direction depending upon theposition of switch 65. Condenser 61 is provided to smooth out thecurrent fiow through the winding 68.

When the switch 65 is in its upper position, the current flow throughthe winding 68 is in the same direction as the current through otherwinding of the choke coil 66 due to the .8 battery 33. Any increase insound strength causes an increase in the current flowing through thecoil 68. This will further saturate the iron core of choke coil 66,decreasing its permeability and decreasing the reaction of the chokecoil 66 to the output of the amplifier tube 24. This will cause agreater sound current to flow through the choke coil 66 which willdecrease the voltage impressed upon the next amplifier tube 21, which inturn will decrease the gain ratio of the multi-stage amplifier.

When the switch 65 is in its lower position, the

current through the winding 68 is reversed. In-

this case, increase in signal strength causes an increase in thepermeability of the iron core of choke coil 66 which increases thereactance of this choke coil. This decreases the amount of sound currentflowing through the choke coil,

. which increases the voltage across the next stage 21, which causes anincrease in the gain ratio of the multi-stage amplifier.

It may be noted that the operation of Fig. 4 differs from that of Fig. 1by emphasizing the change of reactance component of coupling impedance,whereas Fig. l emphasizes primarily changes of resistance component ofthe coupling impedance, with the reactance change an incidental efiect.

Thus it will be seen that a multi-stage amplifying system has beenprovided in which the gainratio is controlled by the impedance of theinterstage coupling devices. The impedance is controlled by the dynamicsof the sound impressed upon the amplifier either to compress the volumeratio or expand it.

While certain novel features of the invention have been disclosed andare pointed'out in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in the art without depart ing from the spirit of the invention.

What is claimed is:

1. In a system for use with a phonograph record, a multi-stageamplifier, a coupling device between stages of said amplifier, means forchanging the volume ratio of the sound by varying the said couplingdevice, and a change over device for changing from volume expansion tovolume compression.

2. In an amplifying system for use with a sound record, an amplifiercomprising a first amplifier tube and a second amplifier tube, avariable impedance coupling said tubes, a control tube fed by the soundenergy, a rectifier for rectifying the output of said control tube,means for varying said impedance comprising a control circuit fed bysaid rectifier to vary the gain ratio of the amplifier, and means forreversing the direction of the control current through said controlcircuit to either expand or compress the volume ratio.

3 In a phonographic system, a sound record, a translating deviceassociated therewith, a multistage amplifier connected to saidtranslating device, a second translating device connected to saidamplifier, a transformer coupling between stages of said amplifier, avariable impedance tube having its plate connected across the primary ofsaid transformer coupling and means controlled according to the dynamicsof the sound for varying the impedance of said impedance tube.

4. In a phonographic system, a sound record, a translating deviceassociated therewith, a multistage amplifier connected to saidtranslating device, a second translating device connected to saidamplifier, a transformer coupling between adjoining stages of saidamplifier, a resistance across the secondary of said transformercoupling, said resistance comprising a fixed resistance and the platecircuit of a control vacuum tube in series therewith, and meanscontrolled according to the dynamics of the sound for varying theimpedance of said tube.

5. In a phonographic system, a sound record, a translating deviceassociated therewith, a multistage amplifier connected to said device, asecond translating device connected to said amplifier, an impedancecoupling between adjoining stages of said amplifier, said impedancecoupling having an iron core and a secondary winding and meanscontrolled according to the dynamics of the sound for controlling thesaturation current through said secondary winding.

6. In a phonograph system, a first translating device, a secondtranslating device, a circuit between said devices, a coupling impedancein said circuit, and control means for varying the value of saidimpedance, said control means being governed by a moving average of theenergy fed to said circuit by the first translating device.

'7. In a phonograph system, a first translating device, a secondtranslating device, a circuit between said devices, a coupling impedanceshunt across said circuit, and control means for varying the impedancevalue of said shunt, said control means being governed by a movingaverage of the energy fed to said circuit by the first translatingdevice. v

8. In a phonograph system, a first translating device, asecondtranslating device, a circuit between said devices, a couplingtransformer in said circuit, a resistance shunt across the primary ofsaid transformer, and control means for varying the value of saidresistance shunt, said control means being governed by a moving averageof the energy fed to said circuit by the first translating device. i

9. In a phonograph system, a first translating device, a secondtranslating device, a circuit between said devices, a transformer insaid circuit, a resistance shunt across the secondary of saidtransformer, and control means for varying the resistance of said shunt,said control means being governed by a moving average of the energy fedto said circuit by the first translating device.

10. In a phonograph system, a first translating device, a secondtranslating device, a circuit between said devices, an inductance shuntacross said circuit, said shunt comprising a winding having a core ofmagnetic material and means for varying the saturation of said core,said means being governed by the moving average of the energy fed tosaid circuit by the firsttranslating device.

11. In a phonograph system, a first translating device, a secondtranslating device, a circuit between said devices, an impedance in saidcircuit and control means for varying the value of said impedance, saidcontrol means being governed by a moving average of the energy fed tosaid circuit by the first translating device, the action of said controlmeans being reversible.

12. The method of transferring sound to or from a sound record whichcomprises varying" sound record and expanding the dynamics of the soundwhich comprises translating the sound variations on the record intocorresponding electrical variations, amplifying said electricalvariations, passing said electrical variations through a variablecoupling device, then further amplifying said electrical variations,translating the electrical variations as thus amplified intocompressional sound waves, rectifying a portion of the electricalvariations, and controlling the tightness of said coupling devices bysaid rectified electrical variations.

14. In a sound reproducing system, a sound record, a pick-up devicetherefor, a multi-stage least two vacuum tube stages having couplingdevices between stages, a control channel fed by said pick-up device forcontrolling the gain of said amplifier, said control channel comprisinga rectifier for producing a sub-audio control current, and means forcausing said sub-audio control current to vary the tightness of acoupling device according to the moving average of the sound energy toexpand the volume range of the audible signal.

JOHN HAYS HAMMOND, JR.

